This application claims the priority benefit of Taiwanese application Ser. No. 90120811, filed on Aug. 24, 2001.
1. Field of the Invention
This invention relates to a method of accessing memory of de-interleaving unit in an optical disc device.
2 Description of Related Art
To increase the reliability of read operation on a CD-ROM (Compact-Disc Read-Only-Memory) drive, data are interleaved before they are recorded on a CD-ROM disc. Therefore, the read operation in the CD-ROM drive should include a de-interleaving procedure. FIG. 1 is a schematic diagram showing a series of functional units involved in a read operation in the CD-ROM drive, which includes an EFM demodulation unit 102, a C1 decoding unit 104, a de-interleaving unit 106, and a C2 decoding unit 108. The EFM demodulation unit 102 is capable of demodulating data on the disc into a stream of 8-bit data. After the C1 decoding unit 104 receives a frame of 32 bytes (8-bit) data from the EFM demodulation unit 102, it decodes them into a frame of 28 bytes data and then transfers these decoded data to the de-interleaving unit 106 for de-interleaving. The de-interleaving unit 106 then transfers the de-interleaved data to the C2 decoding unit 108. During the de-interleaving procedure, each frame includes 28 bytes of data.
The de-interleaving unit 106 includes a memory unit for the de-interleaving process. FIG. 2 shows the memory allocation for the memory of the de-interleaving unit 106. Referring to FIG. 2 together with FIG. 1, the address range is from 0 to 3051. The 28 8-bit (byte) data in the first frame from the C1 decoding unit 104 are respectively denoted by (f0, 0), (f0, 1), . . . , (f0, 27). When the C1 decoding unit 104 transfers the first frame to the de-interleaving unit 106, data in the first frame are written into the memory of the de-interleaving unit 106 in such a manner according to the conventional access method as following. The first data (f0, 0) is written into Row 108 Column 0(i.e., the address 3024); the second data (f0, 1) is written into Row 104 Column 1(i.e., the address 2913); and so forth, the last data (f0, 27) is written into Row 0 Column 26 (i.e., the address 27).
After the first frame is written completely, the second frame is then written into the de-interleaving unit 106. In the following, the 28 8-bit data in the second frame from the C1 decoding unit 104 are respectively denoted by (f1, 0), (f1, 1), . . . , (f1, 27). When the C1 decoding unit 104 transfers the second frame to the de-interleaving unit 106, data in the second frame are written into the memory of the de-interleaving unit 106 in such a manner according to conventional access method that the first data (f1, 0) is written into Row 109 Column 0(i.e., the address 0); the second data (f1, 1) is written into Row 105 Column 1(i.e., the address 2914); and so forth the last data (f1, 27) is written into the Row 1 Column 26(i.e., the address 55). The similar procedure is repeated for each of the subsequent frames.
When a certain row in the memory of the de-interleaving unit 106 is fully rewritten by the decoded data, the de-interleaving unit 106 will then output all the data stored in that row to the C2 decoding unit 108. For example, when Row 108 is fully rewritten, the de-interleaving unit 106 will output all the data stored in Row 108 to the C2 decoding unit 108. In other words, when address 3051 (Row 108 Column 27) is rewritten by (f108, 27), all data stored in Row 108, including 0(f0, 0), (f4, 1), (f8, 2), . . . and (f108, 27) will be transferred to the C2 decoding unit 108.
One drawback to the forgoing memory access scheme, however, is that the memory of the de-interleaving unit 106 is ineffectively utilized (i.e., some memory locations are unused during the de-interleaving process). By the conventional memory access scheme, it requires a total of 109*28=3052 bytes of memory space for the de-interleaving process, which is considerably large and thus is cost-ineffective in memory utilization.
It is therefore an objective of this invention to provide a method of accessing the memory of a de-interleaving unit, which allows effective use of the memory space of the de-interleaving unit to save cost.
The proposed method according to the invention utilizes a special access method to write into and read from the memory of the de-interleaving unit. The write operation is formulated for the purpose of storing a sequence of frames of data from a decoding unit at address locations specified by Write Memory Address WMA based on Write Frame Index WFIDX and Control Word Count CWCNT. The read operation according to the invention is formulated for the purpose of reading a sequence of de-interleaved frames of data from the memory of the de-interleaving unit specified by Read Memory Address RAM based on Read Frame Index RFIDX and Control Word Count CWCNT.
The method according to the invention reduces the required memory space in the de-interleaving unit by half as compared to the prior art for performing a de-interleaving process and is therefore more cost-effective t than the prior art.